This invention relates to window coverings that are hung from a headrail in which are stored the cords that lift the window covering. Cords to be stored inside headrails are commonly wound, as the blind is raised, onto spools that are mounted on a rotating shaft. Or the cords are wound onto the rotating shaft itself.
Where rotating shafts are used, the shaft is usually caused to move in the axial direction so that the cords wind in a single layer thereupon. The axial movement is caused either by means of a screw or by the mechanism disclosed in U.S. Pat. No. 4,623,012. Screw mechanisms ordinarily have a built-in stop that is actuated by the advance of the screw itself. The mechanism of U.S. Pat. No. 4,623,012 normally does not require a stop because the cords can be wound onto the shaft in either direction. However, various types of operating mechanisms are used with shaft-winding systems and some of these are easier to operate in one direction than in the other. This difference becomes greater for heavier blinds. For these situations, a bottom stop is desirable so that one direction of rotation is always used for lifting the blind.
While it is possible to add a screw actuated stop to any rotating shaft mechanism, it is desirable that the stop be perfectly coordinated with the unwinding of the lift cords so that the stop is actuated just as the cords become fully unwound from the shaft.